24. Melting of wax is a physical change but burning of wax is a chemical change. Explain.
Answers
The composition of the wax did not change and no new substance was formed.melting the wax doesn't change the chemical composition of the wax but when we burn wax the chemical composition of the wax changes.
A burning wax (candle)is an example of a chemical change because the paraffin wax, which is a hydrocarbon, undergoes a chemical reaction with oxygen to form water and carbon dioxide gas.
Question
The diameter of a semicircular table is 10 cm. Find the cost of polishing the semicircular table at the rate of ₹3.50 per sq.cm.
Answer
Diameter of a semicircular table = 10cm
Radius of the semicircular table
\begin{gathered} = (\frac{diameter}{2} ) \\ = ( \frac{10}{2} )cm \\ = 5cm\end{gathered}
=(
2
diameter
)
=(
2
10
)cm
=5cm
Area of the semicircular table
\begin{gathered} = (\frac{\pi {r}^{2} }{2}) \\ = ( \frac{22}{7} \times 5 \times 5 \times \frac{1}{2} ) {cm}^{2} \\ = 39.285 {cm}^{2} \end{gathered}
=(
2
πr
2
)
=(
7
22
×5×5×
2
1
)cm
2
=39.285cm
2
Cost of polishing the semicircular table at the rate of ₹3.50cm²
\begin{gathered} = ₹(39.285 \times 3.50) \\ = ₹137.4975\end{gathered}
=₹(39.285×3.50)
=₹137.4975
More Information
Surface Area of Cuboid = 2(lb+bh+lh)
Surface Area of Cube = 6(side)²
Area of four walls = 2(l+b)h
Lateral Surface Area of Cuboid = 2(l+b)h
Lateral Surface Area of Cube = 4(side)²